The Food and Drug Administration was dragged into the online world of medical misinformation this week, telling consumers not to drink bleach solutions that are being marketed as cures for autism, cancer, H.I.V./AIDS and other medical conditions.

It was the latest example of how health authorities must sometimes pit science against the viral power of the internet, which regularly serves as a platform for inaccurate medical advice and unproven claims of breakthroughs.

The F.D.A. has previously taken a stand against the “cruel deception” of supposed cures for cancer, the “dangerous scam” of bee pollen products for weight loss and claims that a dietary supplement can treat a concussion (“No!”).

In a statement on Monday, the F.D.A. said it first told consumers not to drink the bleach products in 2010. But its hand was forced again after the products continued to be promoted on social media and sold online by independent distributors, and the agency recently received new reports of people being sickened.

“Ingesting these products is the same as drinking bleach,” said the F.D.A.’s acting commissioner, Dr. Ned Sharpless. “Consumers should not use these products, and parents should not give these products to their children for any reason.”

The F.D.A.’s statement referred to products that use the names Miracle or Master Mineral Solution; Master Mineral Supplement; Water Purification Solution; Chlorine Dioxide Protocol; and MMS. Generally, they are composed of a solution of sodium chlorite and distilled water, with instructions for consumers to add citric acid, which turns them into a powerful bleaching agent.

The distributors, who were not named in the statement, claim the result is an “antimicrobial, antiviral and antibacterial” remedy for autism, cancer, H.I.V./AIDS, hepatitis, the flu and other conditions, the F.D.A. said.

But such claims are “false” and “dangerous,” the agency added.

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An illustration put out by the F.D.A. warned against the bleach solutions that are being marketed as medical cures. CreditU.S. Food and Drug Administration

Its advice to those who are drinking it: “Stop now.”

Consuming the solution is comparable to drinking the active ingredients in disinfectants and can cause nausea, vomiting, diarrhea and severe dehydration, the F.D.A. said.

The American Association of Poison Control Centers said in its annual reports that 226 cases of exposure to non-household bleach were reported to national poison control centers in 2017, the most recent year for which data was available, compared with 276 in 2016. The data did not include whether the exposure was accidental or intentional, or whether it resulted in fatalities.

But the problem could be wider: Experts say that not everyone who is exposed to the solution will report it, because the labels on such products say that vomiting and diarrhea are common side effects.

“This is a pretty rare exposure, and that might be that people are afraid of being judged,” Dr. Kelly Johnson-Arbor, a medical toxicologist and a medical director at the National Capital Poison Center in Washington, D.C., said in an interview. “All this data is underreported, because somebody has to decide to call the poison center or make the report to the F.D.A.”

Dr. Sharpless said his agency would track the companies selling the products and “take appropriate enforcement actions.” In 2015, a federal jury in Washington State found a Spokane man, Louis Daniel Smith, 45, guilty of selling industrial bleach as a “miracle cure,” the Justice Department said.

The F.D.A. has warned and taken action against companies promoting other products purported to be used as a treatment for autism, including cleanses, detoxifying clay baths and hyperbaric oxygen therapy.

“Unfortunately, there are a large number of online groups that spread general misinformation about autism,” said Thomas W. Frazier, the chief science officer at Autism Speaks, an advocacy organization that sponsors research and carries out awareness and outreach efforts. “These range from fairly benign observations about diet that lack evidence to ‘miracle cures’ that could carry significant risk.”

The dangers of medical misinformation were highlighted in an investigation by NBC News that was published in June and examined online attempts to encourage the use of chlorine dioxide to treat autism, which has no known cure.

This year, Amazon removed online listings for two books that claim to contain cures for autism, one of which, “Healing the Symptoms Known as Autism,” recommends that children with autism drink and bathe in chlorine dioxide.

That kind of online medical misinformation continues to pose challenges for the F.D.A. as it tries to block distributors of unapproved drugs that are marketed as cure-alls.

“These folks can move incredibly quickly,” said Dr. Peter Lurie, the president of the Center for Science in the Public Interest, a nonprofit group. “They can put up the website much more quickly than the F.D.A. can act to take it down. The F.D.A. is always playing catch-up.”

Christine Hauser is a reporter, covering national and foreign news. Her previous jobs in the newsroom include stints in Business covering financial markets and on the Metro Desk in the police bureau. @ChristineNYT

A version of this article appears in print on , Section A, Page 19 of the New York edition with the headline: Whatever Ails You, F.D.A. Says, Drinking Bleach Isn’t the Answer. Order Reprints | Today’s Paper | Subscribe